dispatch_io_create(3) on macOS

The text e826f0cc4ab1, as Mac OS X 10.8.5, Mac OS X 10.8.4, Mac OS X 10.8.3, Mac OS X 10.8.2, Mac OS X 10.8.1, Mac OS X 10.8 shipped it.

open, close and configure dispatch I/O channels

dispatch_io_create(3) on macOS now